Researchers Spot Giant Sharks off Corcovado

March 20, 2009

Researchers with the ocean conservation organization PRETOMA were pulling in their fishing line when they realized they had caught a little more than they had bargained for: what is believed to be a bull shark measuring approximately four meters (13 feet) in length.

“It was very close to the surface. We were pulling it in when the line broke,” said Allan Bolaños, a researcher who was aboard a boat about two kilometers off the coast of the southern PacificOsaPeninsula when he and others spotted the massive shark.

Bolaños and a group of researchers were in the region to capture bull sharks in order to outfit them with tracking devices in order to study their movements. The fishing lines the scientists were using, however, were no match for the largest of these sharks, PRETOMA said in a statement released last week.

“Many of the hooks and steel leaders were mangled, destroyed, or simply bitten off by the large animals, only one of which came close enough to our fishing vessel for us to take a glimpse of its amazing size, before it too broke free,” said Randall Arauz, the expedition’s scientific director.

Bull sharks, particularly juveniles, are known to swim up freshwater rivers in search of food and protection. Bull sharks have been seen far up the San Juan River, which forms Costa Rica’s northern border with Nicaragua, and are believed to inhabit Lake Nicaragua, the river’s source.

On average, bull sharks range between 2.1 and 3.4 meters, and are classified as “near threatened” by the International Union for the Conservation of Nature (IUCN).

As part of the Bull Shark Tagging Project, the researchers captured and tagged four juvenile bull sharks measuring approximately one meter in the brackish waters where the SirenaRiver meets the ocean, at the edge of CorcovadoNational Park. Bolaños and others are studying the movement patterns of the sharks in the hopes of expanding the national park’s boundaries to cover more of the sea.

Currently, Bolaños said, the park’s protected status extends 500 meters into the ocean, an area where fishing is prohibited. The four-meter bull shark was spotted two kilometers from shore.

The research project is funded by the Whitley Fund for Nature (WFN), the BBC Wildlife Fund and corporate sponsors through PRETOMA’s Corporate Membership program.

–Leland Baxter-Neal

 

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